The present application is submitted in response to the NHLBI RFA: Purification of Erythropoietin. We wish to design and develop a simple and effective procedure for the purification of erythropoietin. We hope to prepare homogeneous material with high yield and low cost in a minimum amount of time. Our proposed procedure consists of two main steps, which are designed for maximum specificity and stability of the erythropoietin, based on its known molecular properties: (1) We shall use a unique double-binary complex affinity chromatography as a specific step for purification. Con A-Sepharose shall be used as an alpha-D-manosyl and alpha-D-glucosyl group-specific absorbant for glycoproteins and Cetyl-pyridinium chloride shall be used as a specific ligand for sialated erythropoietin, and will thus promote its exclusive elution. (2) We shall use hydrophobic chromatography with decreasing ammonium sulfate concentration as an additional step of purification. This step has a dual-functional purpose: (a) to recover free erythropoietin from its cetylpyridinium complex, and (b) to provide further purification by a combined effect of hydrophobic interaction and solubility fractionation.